1. Field of the Invention
The present invention relates to a method for aligning two objects, a method for detecting a superimposing state of two objects, and an apparatus for aligning two objects. For example, in a probe apparatus, in order to inspect the electric characteristics of an object to be inspected, it is necessary to allow a plurality of electrodes of the inspected object such as a wafer to electrically come into contact with a plurality of contacts (referred to as probes) of a probe card. The present invention relates to a method for aligning the respective electrodes of the inspected object with the respective contacts to realize the contact.
2. Description of the Related Art
Referring to FIGS. 6A and 6B, for example, the probe apparatus comprises a loader chamber 1 to/from which a wafer is delivered and a prober chamber 2 in which the electric characteristics of the wafer delivered from the loader chamber 1 is inspected. The loader chamber 1 comprises a cassette setting portion 3 on which a cassette C receiving a wafer W therein is set, a delivery mechanism (fork) 4 for delivering the wafer W to the loader chamber 1, and a sub chuck 5 for pre-aligning the wafer on the basis of the orientation plane of the wafer while the fork 4 delivers the wafer. The prober chamber 2 includes a setting table (hereinbelow, referred to as main chuck) 6 on which the pre-aligned wafer is set and which is moved in X, Y, Z, and θ directions, a mechanism (alignment mechanism) 7 for accurately positioning the wafer on the main chuck 6, and a probe card 8 having probes 8A. The probe card 8 is fixed to a head plate 2A arranged on the top of the prober chamber 2.
As shown in FIGS. 6A and 6B, the alignment mechanism 7 has a lower CCD camera 7A and an upper CCD camera 7B. The alignment mechanism 7 is controlled by a control device (not shown). The lower CCD camera 7A is provided for the main chuck 6. The lower CCD camera 7A photographs the probes 8A of the probe card 8 from the underside. The upper CCD camera 7B is arranged on the center of an alignment bridge 7C. The upper CCD camera 7B photographs the wafer W on the main chuck 6 from the above side. The photographed images of the probes 8A and wafer W are displayed on a monitor screen 9A of a display device 9. The alignment bridge 7C is moved from the inmost portion (the upper portion in FIG. 6B) of the prober chamber 2 to a probe center along a pair of guide rails 7D arranged in the Y direction in the upper portion of the prober chamber 2. The main chuck 6 has a target 7E which is movable above the lower CCD camera 7A. The optical axis of the lower CCD camera 7A matches the optical axis of the upper CCD camera 7B through the target 7E. The position of the main chuck 6 upon matching is used as a reference position for alignment of the wafer W and the probes 8A.
The prober chamber 2 has a rotatable test head T. The test head T is electrically connected to the probe card 8 through an interface portion (not shown). A signal for inspection is transmitted from a tester to electrode pads of the wafer via the test head T and the probes 8A.
The alignment of the probes 8A of the probe card 8 and the electrode pads of the wafer W will now be described. The upper CCD camera 7B and the lower CCD camera 7A photograph a plurality of probes 8A as targets for alignment (hereinbelow, referred to as target probes) and a plurality of electrode pads corresponding thereto (hereinbelow, referred to as target electrode pads). The optical axis of the upper CCD camera 7B arranged at the center of the probes is allowed to match the optical axis of the lower CCD camera 7A fixed to the main chuck through the target 7E. The position at that time is set to the reference position of the main chuck 6. On the basis of the position coordinates of each target probe 8A and the reference position coordinates in the photographing position, the amount of deviation between the target probe 8A and the reference position is calculated. Similarly, the amount of deviation between each target electrode pad and the reference position is also calculated. On the basis of the deviation amounts of the plurality of target electrode pads from the reference position, the position coordinates where the target probes 8A match the target pads are calculated. The main chuck 6 is moved on the basis of the calculation results to align the target probes 8A with the target electrode pads.
In conventional aligning methods, however, on the basis of position data of the target probes 8A, the position data of the target electrode pads, and the reference position of the main chuck 6, and the amount to move the main chuck 6 has to be obtained for every target probe and every target pad. Accordingly, the calculation process is complicated. In association with the super integration of devices, the desired alignment precision becomes higher. Consequently, the calculation for alignment becomes more complicated, so that the throughput of the inspection is deteriorated.